1. Field of the Invention
This invention relates generally to a two-dimensional address or matrix device, and is more particularly directed to a two-dimensional display device employing liquid crystals.
2. Description of the Prior Art
It has been previously proposed to display a television picture on a liquid-crystal display device. Normally, such a device employs a plurality of picture element units disposed in an X-Y array or matrix, with each picture element unit being formed of a liquid crystal cell and a switching element, which can be an FET. Generally, the picture element units are arranged in n horizontal rows and m vertical columns. A horizontal scanning pulse generator, normally formed of a shift register, has m output terminals and cycles once for each horizontal line interval of an input video signal, so each of the m outputs is high for a fraction 1/m of the picture portion of a horizontal line interval. A vertical scanning pulse generator, normally formed as a shift register, has n output terminals, and cycles once each frame interval (i.e., odd output terminals are made high in turn during odd field intervals, and even output terminals are made high in turn during even field intervals).
Vertical signal transmitting lines are respectively connected to all of the n switching elements of each column, and horizontal signal transmitting lines are respectively connected to each of the m switching elements of each row. Each of the m vertical lines is connected to an output terminal of a respective input switching element, which has an input terminal connected to a signal input to receive a video input signal and has a control electrode connected to a respective one of the m output terminals of the horizontal scanning pulse generator. The n horizontal lines are each connected to a respective one of the n output terminals of the vertical scanning pulse generator.
At any given moment, the input video signal is applied to a single one of the picture element units, namely, that one for which the horizontal and vertical scanning pulses are both high. Each of the liquid crystal cells has a signal charge imparted to it, in turn, and the optical transmissivity of each such liquid crystal cell is governed by its respective signal charge.
A new signal charge is given to each liquid crystal cell during each video frame.
The liquid crystal display device so constructed presents a video picture formed of a mosaic of these cells, each having a particular optical transmissivity as governed by the level of the video signal at the time that the associated vertical and horizontal scanning pulses are both high.
Each of the liquid crystal cells is formed as a capacitor with a liquid crystal layer sandwiched between a flat, transparent target electrode and a flat picture element electrode, with the same being connected by its respective switching element to the associated vertical signal transmitting line. The latter runs parallel to the picture element electrode and is separated therefrom by an insulating oxide layer. The liquid crystal cells each have a memory capacity C.sub.M for storing the signal charge applied thereto. Unfortunately, there is also a parasitic capacitance C.sub.S between the vertical signal transmitting lines and the liquid crystal elements.
Consequently, when an input signal charge, corresponding to a particular picture element of a video picture, is applied to a particular one of the liquid crystal cells for which the vertical and horizontal scanning pulse signals are both high, the parasitic capacitance C.sub.S causes a crosstalk signal to be applied to the remaining liquid crystal cells in each vertical column (for which cells the vertical scanning pulse signal is low). This signal has a level which is a factor EQU C.sub.S /(C.sub.S +C.sub.M)
times the level of the video input signal.
As a result of this crosstalk, if a bright or dark object appears in the video picture, light or dark vertical bars can appear on the display device emanating upward or downward from the object. This objectionable result occurs as a result of the structure of the conventional liquid crystal display device, and cannot be avoided merely by processing the video signal applied thereto.